[Caching] Clear benign CodeGen options when building modules

Use `resetBenignCodeGenOptions()` from clang dependency scanner to clear
the swift explicit module build cc1 arguments. This fixes the problem
that CurrentWorkingDirectory is leaking through
`-fcoverage-compilation-dir` that can cause extra module variants when
caching is enabled. This also avoid the duplicating the logics for
clearing CodeGen options inside Swift.

rdar://151395300

Author: cachemeifyoucan

lib/ClangImporter/ClangImporter.cpp

@@ -90,6 +90,7 @@
 #include "clang/Serialization/ASTReader.h"
 #include "clang/Serialization/ASTWriter.h"
 #include "clang/Serialization/ObjectFilePCHContainerReader.h"
+#include "clang/Tooling/DependencyScanning/ModuleDepCollector.h"
 #include "clang/Tooling/DependencyScanning/ScanAndUpdateArgs.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/ADT/STLExtras.h"
@@ -4232,11 +4233,12 @@ ClangImporter::getSwiftExplicitModuleDirectCC1Args() const {
   PPOpts.MacroIncludes.clear();
   PPOpts.Includes.clear();
 
-  // CodeGenOptions.
-  auto &CGOpts = instance.getCodeGenOpts();
-  CGOpts.DebugCompilationDir.clear();
+  // Clear benign CodeGenOptions.
+  clang::tooling::dependencies::resetBenignCodeGenOptions(
+      clang::frontend::ActionKind::GenerateModule, instance.getLangOpts(),
+      instance.getCodeGenOpts());
 
-    // FileSystemOptions.
+  // FileSystemOptions.
   auto &FSOpts = instance.getFileSystemOpts();
   FSOpts.WorkingDir.clear();
 

test/CAS/coverage-dir.swift

@@ -0,0 +1,28 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -scan-dependencies -module-name Test -O -I %t/include \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   %t/main.swift -o %t/deps.json -cache-compile-job -cas-path %t/cas -profile-coverage-mapping -profile-generate
+
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:SwiftShims > %t/shim.cmd
+// RUN: %swift_frontend_plain @%t/shim.cmd
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json A > %t/A.cmd
+// RUN: %swift_frontend_plain @%t/A.cmd
+
+// RUN: %FileCheck %s --input-file=%t/shim.cmd
+// RUN: %FileCheck %s --input-file=%t/A.cmd
+
+// CHECK: -direct-clang-cc1-module-build
+// CHECK-NOT: -fcoverage-compilation-dir
+
+//--- main.swift
+import A
+func test() {
+  a();
+}
+
+//--- include/A.swiftinterface
+// swift-interface-format-version: 1.0
+// swift-module-flags: -module-name A -O -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib -user-module-version 1.0
+public func a() { }